Method and device for providing a minimum congestion flow of ethernet traffic transported over a SDH/SONET network

ABSTRACT

Disclosed is a method for providing a minimum congestion flow of Ethernet traffic that is transported through a pipe from a sending point to a receiving point over at least one SDH/SONET network, the at least one SDH/SONET network comprising network elements, fiber connections connecting the network elements and SDH/SONET virtual containers, the transport being managed through a new layer over SDH/SONET network physical layer, the new layer comprising Access Points, links of Access Point pairs and circuits, namely the possible routes for connecting a pair of Access Points. The method further comprising: generating a delay marker at the network element of the sending point; transmitting the delay marker to the network element of the receiving point and back to the network element of the sending point through at least one Circuit; calculating the time frame for the sending point network element to receive back the delay marker; and estimating the congestion of the Circuit according to the time frame for receiving back the delay marker.

INCORPORATION BY REFERENCE OF PRIORITY DOCUMENT

[0001] This application is based on, and claims the benefit of, EuropeanPatent Applications No. 02290445.2 filed on Feb. 22, 2002 and 02291993.0filed on Aug. 8, 2002, which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the telecommunication field andin particular to the transport of Ethernet frames over a transportSDH/SONET network. Still more in particular, the present inventionrelates to a method and device for providing a minimum delay dispatchingof Ethernet traffic frames over the SDH/SONET network.

[0004] As it is known, traffic generated by an Ethernet apparatus ischaracterized by discontinuities, namely there are periods with a moreor less constant sending rate of Ethernet packets and periods duringwhich a rather long time is provided between a received Ethernet frameand the next one. Such unstable/inconstant traffic is generally termed“bursty”. On the contrary, SDH or SONET traffic is characterized by aconstant sending/receiving rate. In other words, any network element ofa transport SDH/SONET network sends corresponding frames with a regularand constant rate. Furthermore, Ethernet frames do not have a fixedlength/size but only a maximum size (1518 bytes).

[0005] It is easy to understand that these discrepancies result in ahighly difficult interfacing of two technologies having differentnatures/characteristics.

[0006] 2. Description of the Prior Art

[0007] An already available solution to the above problem allows themapping of Ethernet frames into SDH/SONET Virtual Containers as atransparent tributary; all incoming bits are transported to the outputinterface with the related timing information (frequency for recoveringthe proper bit rate at the reception side). Within the SDH/SONET payloadalso the dead times between a received Ethernet frame and the followingone are mapped.

[0008] The general problem of transporting Ethernet frames over aSONET/SDH transport network is presently solved through SONET/SDHvirtual concatenation. Ethernet frame transport is performed accordingto the following main steps: the bytes of one frame are distributedamong all the available SDH/SONET Virtual Containers, namely, the firstframe byte is mapped in the first VC, the second frame byte is mapped inthe second VC and so on; due to the fact that SDH/SONET VirtualContainers can follow different paths, at the ending point, the VirtualContainers should be realigned; and the bytes of the Ethernet frames areextracted from the realigned Virtual Containers and the frame is finallyre-assembled.

[0009] At present, when Ethernet traffic is transported over SDH/SONETnetworks, some queues of Ethernet frames are required. The Ethernetframes should be transported over SDH/SONET network throughpoint-to-point connections. As a point-to-point connection could beaccomplished by means of different routes connecting the starting andending points, the problem to solve is to find the best route in termsof transport and network performances.

[0010] As far as the inventors are aware, there is no known solution tothis problem and the frames are transmitted through fixed point-to-pointconnections, regardless whether the resources which are intended for thetransport are overused and some other resources (which could provide areduced dispatching time) are underused.

[0011] The above problem could become even worst when there is a faultof the SDH/SONET Virtual Containers transporting the Ethernet frames. Atpresent, faults are managed according to the relevant SDH/SONETRecommendations but, in many case, a fault affecting a Virtual Containerassigned to the transport of Ethernet frames leads to a complete loss ofthe traffic.

SUMMARY OF THE INVENTION

[0012] In view of the above main problem, the general object of thepresent invention is overcoming it in an efficient manner.

[0013] The main object of the present invention is providing a methodand device which is able to find out the minimum delay route fordispatching frames from a starting point to an ending point. The minimumdelay dispatching feature results in being particularly advantageouswhen the network capacity is reduced because of a fault of one or moreVCs.

[0014] An additional object of the present invention is providing such amethod that could be implemented in hardware.

[0015] The above and further objects of the present invention areobtained by a method according to claim 1 and from a device according toclaim 10. Further advantageous features of the present invention are setforth in respective dependent claims. All the claims should beconsidered as an integral part of the present description.

[0016] The basic and general idea of the proposed solution is to assignthe frame to the Circuit that can perform the transport with the minimumdelay.

[0017] The Link transmitter continuously monitors the congestion ofevery Circuit and assigns every frame to the current fastest Circuitaccording to the last available congestion evaluation. The applicationof the minimum delay criterion leads to the best possible balance amongall the available Circuits; the congestion of all the Circuits should bemore or less the same. The optimisation of Circuit congestion leads tothe optimisation of network congestion too.

[0018] The present invention operates through a new layer/network whichis provided over the SDH/SONET network in order to manage the transportof Ethernet traffic over SDH/SONET network; this new layer/network usesthe resources of SDH/SONET network in such a way as to optimize theprovided services and the performances with reference to this specifictype of transport. Such a new layer has been fully disclosed and claimedin a previous patent application (EP02290445.2) of the same applicant.The content of it is fully incorporated herewith as a reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will become clear in view of the followingdetailed description, to be read having reference to the attached sheetsof drawings, wherein:

[0020]FIG. 1 shows the structure of a exemplifying Virtual PrivateNetwork; and

[0021]FIG. 2 highlights a Link, with two related Circuits, selected fromthe network of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] As said above, the present invention operates in a layer/networkwhich is termed NETS (i.e. Network of Ethernet Transport over SDH/SONET)and is disclosed in EP02290445.2 The NETS comprises basic elements thatare listed below for a better comprehension of the present invention.

[0023] The NETS model comprises five basic elements: Access Point, Link,Circuit, Pipe and Path. An Access Point (AP) is an Ethernet interface atthe boundary of an SDH/SONET network; it is the point where the Ethernettraffic can access/leave the SDH/SONET network. FIG. 1 depicts a simpleexample of network comprising five Network Elements (NE #0 to NE #4)with each network element having an Access Point: NE #0 has AP #0, NE #1has AP #1, NE #2 has AP #2, NE #3 has AP #4 and finally NE #4 has AP #3.Naturally, a Network Element can host more than one Access Point.

[0024] A pair of Ethernet Access Points defines a point-to-pointconnection; this connection is named Link. For instance, with referenceto FIG. 1, the pair AP #0 & AP #1 identifies a link; the pair AP #2 & AP#4 defines another link, and so on.

[0025] An SDH/SONET network could allow for the connection of two AccessPoints (i.e. to accomplish a Link) by means of different routes; everyroute is named Circuit. A Circuit is obtained by a Pipe concatenationand could be considered as a series connection of N Pipes.

[0026] In its turn, every Circuit/route that connects two Access Pointscan be divided into a sequence of smaller segments; every segment isnamed Pipe.

[0027] The basic pipeline is the Virtual Container that connects twoNetwork Elements; it is named Path.

[0028] With reference to FIG. 1, there are two direct routes made up by5×VC-12 and 1×VC-3, respectively, that connect AP #0 and AP #1; thefirst route is named Circuit A and the second one is named Circuit B.Many other routes can connect the two Access Points but, for the aim ofthis example, just two of them are sufficient.

[0029]FIG. 2 highlights the selected Link with the two related Circuits.The direction from NE #0 to NE #1 will be considered first; of coursethe solution is applied to both directions.

[0030] Ethernet frames received at AP #0 are stored in the queue of theLink transmitter LTX₀ of NE #0. Every frame has to be assigned either toCircuit A (VC-12 based) or to Circuit B (VC-3 based) to be transportedover SDH/SONET network to the destination Network Element.

[0031] A frame assigned to a Circuit is stored in the related TX queue(CTX_(A0), CTX_(B0)), transported by means of available VirtualContainers through the SDH network, stored in the RX queue (CRX_(A0),CRX_(B0)) of the Circuit and then provided to the Link receiver LRX₁.

[0032]FIG. 2 does not depict the SDH/SONET nodes (like ADMs or XCs) ofthe network that does not perform the mapping/de-mapping of Ethernettraffic into SDH Virtual Containers.

[0033] The basic and general idea of the proposed solution is to assignthe frame to the Circuit that can perform the transport with the minimumdelay.

[0034] The Link transmitter LTX₀ continuously monitors the congestion ofevery Circuit and assigns every frame to the current fastest Circuitaccording to the last available congestion evaluation. The applicationof the minimum delay criterion leads to the best possible balance amongall the available Circuits; the congestion of all the Circuits should bemore or less the same. The optimisation of Circuit congestion leads tothe optimisation of network congestion too.

[0035] The measurement of Circuit congestion by Link transmitter LTX₀,LTX₁ is mono-directional; the Link transmitter LTX₀ of NE #0 has tomeasure the congestion of Circuit A just along the direction NE#0-NE#1.Similarly, the Link transmitter LTX₁, of NE #1 has the task to measurethe congestion along the opposite direction, namely from NE#1 to NE#0.

[0036] According to a preferred embodiment of the present invention, adelay marker is provided to a Circuit transmitter; advantageously, adelay marker is a bit that has to be transported along the Circuit withan Ethernet frame of the TX queue or a dedicated frame should the TXqueue be empty.

[0037] The task of this bit is to measure the Circuit delay, i.e. itscongestion, along the direction from Link transmitter to Link receiver(for instance, from LTX₀ to LRX₁).

[0038] Every time the Link transmitter provides a delay marker to aCircuit, a timer is started; when this timer is stopped it will providethe measure of the Circuit congestion. The timer is stopped upon receiptof the previously sent delay marker.

[0039] With more specific reference to FIG. 2, let suppose that the Linktransmitter LTX₀ of NE #0 provides the delay marker to Circuit A throughCTX_(A0). Circuit A transports the delay marker to destination. Thetransport delay of the delay marker along Circuit A (from Linktransmitter LTX₀ of NE #0 to Link receiver LRX₁ of NE #1) is the same asfor an Ethernet frame because both of them are stored in the same queuesand transported along the same route.

[0040] As soon as the Link receiver LRX₁ of NE #1 receives the delaymarker from LTX₀, it provides an echo of the delay marker to the Linktransmitter LTX₁ of NE#1. Such an echo of the delay marker is forwardedback to NE#0 along the opposite direction (from NE #1 to NE #0) by usingthe same Circuit A (and/or the other circuit B, if available).

[0041] The task of this echo delay marker is to stop the timer of Linktransmitter LTX₀ in order to have an idea about the Circuit Acongestion.

[0042] The delay of the echo delay marker along the return direction cannot be avoided but two constraints should be complied with for a moreprecise information. In principle, the delay of the echo along thereturn direction should be as short as possible; shorter the returndelay, more precise the measure. Furthermore, this return delay shouldbe the same for every Circuit; in such a way it affects the congestionmeasure for different Circuits in the same way.

[0043] In order to satisfy both these constraints, the echo of the delaymarker is transmitted along the return direction in the following way:

[0044] The delay marker echo has a priority higher than the one ofqueues of frames and skips all possible stored frames. In such a way,the echo delay is decreased.

[0045] The echo is transmitted along the return direction by means ofall the available Circuits (Circuits A and B in FIG. 2). The Linktransmitter stops the timer after the first reception of the echoindependently of the return Circuit that has provided it; this decreasesthe echo's delay again and should guarantee that the return delay shouldbe more or less the same independently of the Circuit under measurement.

[0046] As already stated, the Link transmitter stops the timer uponreception of the first received echo; the value of the stopped timerprovides a measure of Circuit congestion.

[0047] Possibly, an average value of the Circuit congestion iscalculated by taking into account a number N of last measures of thecongestion itself.

[0048] The steps of: issuing a delay marker at the Link transmitter;providing it to Circuit transmitter; receiving it at the Circuitreceiver; providing it to Link Receiver; sending an echo delay markerback to the Link transmitter which issued the delay marker; calculatingthe Circuit congestion; and calculating an average value of Circuitcongestion are continuously repeated for every Circuit.

[0049] Thus, when the Link transmitter LTX₀ has to assign a frame to aCircuit, it applies the minimum delay criterion according to thefollowing steps:

[0050] i. Obtaining the average value of a Circuit congestion. Thisdelay is considered a basic delay that can not be avoided;

[0051] ii. Calculating (by the Link transmitter) the transport delay ofthe frame along this Circuit in the absence of any congestion. This isthe delay requested to transport the frame along the Circuit when thenetwork is unloaded. The frame length (e.g. number of bytes) is dividedby the Circuit capability (e.g. bytes per second) and the result is therequested delay (in seconds). For instance, if a frame of 256 bytes isconsidered, the “unloaded” transport delay of Circuit A is higher thanthe delay of Circuit B because the transport capability of the latterone is more or less five times the capability of Circuit A (a VC-3against 5×VC-12).

[0052] iii. Estimating the future new congestion of the Circuit byadding the current average congestion and the “unloaded” transport delayof the frame.

[0053] iv. Repeating steps i. to iii. for every available Circuit.

[0054] v. Assigning the frame to the Circuit with the minimum estimationof the future congestion.

[0055] Advantageously, the present invention does not simply apply theminimum delay criterion by taking into account the current congestion ofall the available Circuits; profitably, it also takes into account howthe current condition would be modified by assigning the frame to aCircuit or to another one.

[0056] In principle, the Access Points AP #0 and AP #1 of the aboveexample could be connected also by Circuit C that represents the routeNE #0-NE #3-NE #2-NE #1. But Circuit C differs from Circuits A and B atleast for two main reasons, namely because of the presence of twointermediate nodes (NE #3 and NE #2) and for the circuit capability.

[0057] Every intermediate node provides a queue of frames that increasesthe Circuit delay. It is clear that an intermediate node affects the“delay marker” just in terms of a longer delay but the present inventioncan be applied without any problem.

[0058] Circuit C is made up by the sequence VC-3NC-3/5×VC-12; differenttypes of Virtual Containers are used and it is not so clear what is thecapability of the Circuit. An average capability is considered just tosee the Circuit as a pipeline of a fixed section instead of a sequenceof pipelines with different sections; again the proposed solution can beapplied.

[0059] The main advantage of the present invention, as already stated,is that the best possible balance among all the Circuits of a Link couldbe obtained.

[0060] All the Circuits should provide more or less the samecongestion/delay, thus avoiding bottlenecks. This feature also resultsin a limitation of the skew among frames transported along differentCircuits.

[0061] The advantages at network level will become also clearer byconsidering that a Virtual Container can be shared among differentCircuits/Links.

[0062] The VC-3 connecting NE #3 and NE #2 is a part of Circuit C of AP#0-AP #1 link but it can be used as a circuit for AP #4-AP #2 link too.

[0063] A high congestion along this Virtual Container represents abottleneck for both the Links (and the network); the present inventionavoids/limits these conditions by distributing the traffic among thenetwork resources in a homogeneous way.

[0064] The result is an optimisation of the bandwidth of the completenetwork.

[0065] There have thus been shown and described a novel method and anovel device which fulfill all the objects and advantages soughttherefor. Many changes, modifications, variations and other uses andapplications of the subject invention will, however, become apparent tothose skilled in the art after considering the specification and theaccompanying drawings which disclose preferred embodiments thereof. Allsuch changes, modifications, variations and other uses and applicationswhich do not depart from the spirit and scope of the invention aredeemed to be covered by the invention which is limited only by theclaims which follow.

1. A method for providing a minimum congestion flow of Ethernet trafficthat is transported through a pipe from a sending point to a receivingpoint over at least one SDH/SONET network, the at least one SDH/SONETnetwork comprising network elements or nodes, fiber connectionsconnecting the network elements and SDH/SONET virtual containers, thetransport being managed through a new layer over SDH/SONET networkphysical layer, the new layer comprising Access Points, links of AccessPoint pairs and circuits, namely the possible routes for connecting apair of Access Points, wherein the method comprises the steps of:generating a delay marker at the network element of the sending point;transmitting the delay marker to the network element of the receivingpoint and back to the network element of the sending point through atleast one Circuit; calculating the time frame for the sending pointnetwork element to receive back the delay marker; and estimating thecongestion of the Circuit according to the time frame for receiving backthe delay marker.
 2. A method according to claim 1, wherein all thesteps are performed for all the possible Circuits connecting the sendingand receiving points.
 3. A method according to claim 1 or 2, wherein thestep of generating a delay marker at the sending point network elementcomprises the step of generating a delay marker at the Link transmitterof the sending point network element and starting a timer.
 4. A methodaccording to claim 3, wherein the step of transmitting the delay markerto the receiving point network element and back to the sending pointnetwork element through a Circuit comprises the steps of generating adelay marker echo at the Link receiver of receiving point networkelement, forwarding it to Link transmitter of receiving point networkelement, transporting it to the Link receiver of the sending pointnetwork element and finally to the Link transmitter at the sending pointnetwork element to stop the timer.
 5. A method according to claim 4,wherein the step of transporting the delay marker echo to the Linkreceiver of the sending point network element comprises sending the samedelay marker echo through all the available Circuits and skipping anypossible queues of frames in order to reduce the delay of the echo asmuch as possible.
 6. A method according to any of previous claims,wherein the further step of calculating an average value of the Circuitcongestion by taking into account a number of congestion measurementsfor the same Circuit.
 7. A method according to claim 6, wherein thefurther step of calculating an unloaded transport delay of a Circuit bydividing the number of frame bytes by the Circuit capability.
 8. Amethod according to claim 7, wherein a future new congestion of aCircuit is estimated by summing the current average value of the Circuitcongestion with the unloaded transport delay.
 9. A method according toclaim 8, wherein an Ethernet frame to be transported in the SDH/SONETnetwork is assigned to the Circuit with the minimum estimation of thefuture new congestion.
 10. A device for minimum congestion transportingEthernet frame signals in a SDH/SONET network, the SDH/SONET networkcomprising network elements or nodes and fiber connections connectingthe network elements, the device comprising: at least one access pointfor receiving/outputting Ethernet frame signals; a router of thereceived Ethernet frame signals to at least one Link, wherein a link isa pair of Ethernet Access Points providing a point-to-point connectionin the network; a sender of frames to an available Circuit, wherein aCircuit is one of the possible routes connecting the pair of AccessPoints through the network; and an encapsulator of the Ethernet framesignals into at least one Virtual Container of the selected availablePath, wherein said router generates a delay marker which is transmittedto the receiving point and back to the sending point through a Circuit;and wherein a calculator is provided for calculating the time frame forthe sending point to receive back the delay marker; and an estimator isprovided for estimating the congestion of the Circuit according to thetime frame for receiving back the delay marker.
 11. A device accordingto claim 10, wherein said router generates a delay marker furthercomprise a timer that is started when the delay marker is generated orsent.
 12. A device according to claim 11, wherein it further comprises adelay marker for generating a delay marker echo to be forwarded to aLink transmitter of the receiving point, to be transported to the Linkreceiver of the sending point and finally to the Link transmitter at thesending point to stop the timer.